Duplicate photos in catalogue

It depends what you mean by duplicate photos.  In theory, Elements will not import true duplicate images.  However, it will happen in several situations.   Because this shouldn't happen under normal circumstances, using Elements is not the best way to find the duplicates on your computer.  There are other faster and better solutions to finding true duplicate photos.

It would be helpful to figure out how the duplicates ended up in your catalog?  It would also be helpful to know how many duplicates you think there are in the catalog.

For example, if you created a full backup of your catalog, the photo files are copied to the backup location and are given a new name starting with B00.  If you then imported the backup folder into the catalog, you would have duplicate files with that prefix in their names.  It would then be possible to do a search for all such files and deleting them from the catalog.